1. Field of the Invention
The invention relates to a corrosion-protected, self-drilling anchor, a method for the production thereof, and a prefabricated anchor subunit.
2. Description of the Background Art
Ground and rock anchors and piles are used in underground construction whenever it is necessary to transmit forces in the region of the anchor or pile head to deeper soil strata. This applies equally to tension-loaded anchors and nails and to pressure- or tension-loaded piles. For this purpose, anchors, nails, or piles have a supporting member that is brought into a force-fit connection with the surrounding substrate in a borehole and is anchored on the air-side end in the area of the head. Because the supporting members are usually made of steel, they are susceptible to corrosion.
In this context, a distinction is drawn between supporting members for temporary use and supporting members for permanent use, whereby the latter use requires a structural design suitable for protection from corrosion. The terms double or increased corrosion protection are used when passivation of the steel surface of the supporting member is assured by injection of cement grout and an additional plastic tube, surrounding the anchor, represents a diffusion barrier for liquids.
A special case of anchors is the self-drilling anchor whose fields of application are primarily the production of soil nails, micropiles, and temporary anchors. Self-drilling anchors have substantially a number of anchor bolts with a continuous axial hollow space. A drill bit with cleaning nozzles, which are connected via the continuous axial hollow space to a drilling and injection device on the air-side anchor end, is arranged at the end of the first anchor bolt. The self-drilling anchor after the drilling in of a specific anchor bolt is lengthened by the formation of a bell butt joint. If a self-drilling anchor has reached its predefined length, the formed borehole is injected with cement grout via the axial hollow space and, if necessary, the anchor is tensioned after hardening of the grout material.
The advantages of an anchor of this type are first the rapid construction progress achieved by the boring and moving of the anchor and the injection of the borehole in one operation. Therefore, no separate anchor installation and no pipe and rod construction are necessary. The structural design of a self-drilling anchor and the production process determined thereby, however, do not allow the realization of increased corrosion protection necessary for a permanently protected supporting member.